1. Field of the Invention
The present invention relates to a heart stimulator comprising stimulation energy delivering means intended to deliver stimulation energy through at least one implanted lead to the heart of a patient and an atrial arrhythmia detecting means.
2. Description of the Prior Art
There is a 2-4% prevalence of atrial fibrillation in humans around the age of 70 years. In case of chronic atrial fibrillation, paroxysmal atrial fibrillation, and other atrial arrhythmias there is a high risk of medical complications due to possible thrombi formations, such as embolism from the left side of the heart to cerebral arteries or to other arteries of the upper and lower part of the human body. In the case of thrombi formation in the right atrium or ventricle there is also a risk for accompanying embolism to the pulmonary vessels, with a risk of resulting pulmonary embolism.
Patients suffering from atrial arrythmia such as atrial fibrillation are often subject to medication with anti-thrombotic drugs, such as Dicumarol or Warfarine with the accompanying high risks of medical problems. Overdoses are associated with risks of bleeding, bruises and mental problems in relation to the elevated risk of bleeding etc., and undermedication is associated with a too low plasma concentration of Dicumarol and Warfarine with again an obvious risk of thrombi formation.
Moreover, there is a risk of low compliance to self-medication among such patients, who often are elderly. The medication also requires frequent medical check-ups of, e.g. protrombine values, to be able to adapt the level of medication to the needs of the drug metabolism in the individual patient. This means massively increasing medical care expenses. In addition thereto there are in quite a number of clinical cases contraindications to the use of drugs such as the ones mentioned above.
In spite of the frequent usage of the medical treatment described above there is no clear evidence as to the effectiveness of the treatment.
It is traditionally widely accepted that atrial thrombi form only after 2-3 days of atrial fibrillation, and that atrial thrombi in a fibrillating atrium form after the onset of the arrhythmia. Therefore, e.g. cardioversion of atrial fibrillation of less than 3 days duration without anticoagulation prophylaxis is believed to be safe and is commonly performed, see M. F. Stoddard, xe2x80x9cRisk of Thromboembolism in New Onset or Transient Atrial Fibrillationxe2x80x9d, Progress in Cardiovascular Diseases, Vol. XXXIX, No. 1, July/August, 1996, pp. 69-80.
An implantable atrial defibrillator specially designed for keeping the energy consumption on a comparatively low level is described in U.S. Pat. No. 5,433,729, and U.S. Pat. No. 5,464,429 discloses an apparatus for defibrillation of a heart, in which sequences of stimulation pulses and defibrillation shocks are delivered to the heart. The stimulation pulses used have an amplitude and/or pulse duration which greatly exceed the amplitude and/or pulse duration of ordinary pacemaker pulses, however, the high-energy stimulation pulses contain considerably less energy than an ordinary defibrillation shock, thereby reducing the total energy consumption.
In European Application 1 0 727 241 a device for electric heart stimulation is described, which device delivers a mild therapy to achieve an electrical influence on the heart which in a gentle manner reduces the occurrence of malfunctions in the muscles of the heart for correcting or restoring a collapsed conduction system.
In the following electrical thrombosis preventive stimulation or thromboembolic prophylactic stimulation is denoted by TPS and by thromboembolic prophylactic stimulation capture or TPS capture is meant a sufficient stimulation or energy level for achieving supporting hemodynamic blood transportation away from the atrium.
An object of the present invention is to provide a heart stimulator for preventing or reducing thrombosis and embolism occurrence in case of atrial fibrillation or other atrial arrhythmia by administering an electrical therapy, this therapy not being intended for treatment of the atrial fibrillation or atrial arrhythmia in itself.
This object is achieved in accordance with the principles of the present invention in a heart stimulator which, in combination with a conventional pacing regimen, or as a stand-alone therapy, delivers pulses to cardiac tissue with an energy content lower than a conventional defibrillation shock, the energy content of the delivered pulses being sufficient to produce an atrial contraction that promotes the efficiency of hemodynamic blood transportation away from the atrium, thereby preventing thrombi formation in the atrium.
Thus, with the heart stimulator according to the invention an electrical prophylactic therapy is provided by electrical stimulation of heart tissue such that at least a partial contraction of the atrium is achieved with resulting improved hemodynamic blood transportation away from the atrium, where thrombi formation can be initialized. Thus the atrial contraction is not necessarily performed in an optimal physiological manner, but effective enough to protect the patient against thrombi formation and possible left or right sided embolic events. The heart stimulator according to the invention offers a comparatively cheap and easily performed therapy of the above discussed universally spread disease. Another advantage of the heart stimulator according to the invention is that it can be easily realized by modifying existing pacemaker and defibrillator apparatuses.
The heart stimulator according to the invention can suitably be used for providing thromboprophylactic electrical stimulation of the atrium when ordinary defibrillation therapy has not been successful within 2-3 days after the onset of the atrial arrhythmia, as discussed above. The heart stimulator according to the invention can also be used for delivering the thromboprophylactic therapy to patients having chhronic or paroxysmal, non-cureable atrial fibrillation. The therapy delivered by the heart stimulator according to the invention can also be a supplement to thromboprophylactic medication.
The antithrombus stimulation energy pulses delivered by the stimulator according to the invention are of lower energy than a defibrillation shock, but, according to an embodiment of the invention, of sufficient magnitude for causing a contraction in at least a part of atrial muscular tissue. Thus, the thromboprophylactic therapy delivered by the heart stimulator according to the invention is considerably less energy consuming than a regular defibrillation therapy.
According to another embodiment of the heart stimulator according to the invention said stimulator has a control unit which contains synchronizing circuitry which controls the energy delivery stage to deliver antithrombus stimulation energy in a phase of the cardiac cycle sufficiently separated from the vulnerable phase of the cycle. In this way the patient is protected against the triggering of dangerous cardiac events.
The heart stimulator according to the invention can be a pacemaker or a defibrillator having different modes of operation, one of these modes being a thrombo-prophylactic stimulation mode for delivery of antithrombus stimulation energy.